2010 Prius 60,000 MI traction battery won't hold charge

It sure sounds like it's dying but the battery should still be under warranty, have the dealer check it out. Also, it wouldn't hurt to have a OBD2 scanner. I'm planning to buy this one soon.

 

It sounds like your 12 volt battery may be failing. This will create a drag on your HV charge because the inverter is constantly trying to charge the 12 volt. Have you recently left any doors open or lights on in the vehicle for an extended period? Washed the car in acc mode with the radio on?

 

I wouldn't leap to any conclusions. Is there something else creating drag? Tires, etc? IOW, your description sounds more like something's draining it rather than its not charging or holding charge.

 

It's not a leap... 4 years, 60,000 miles is a very good possibility of a failed 12 volt. Especially if it was drained once or twice. That's why I am waiting for the OP to respond...

 

I think Eclipse1701d is right.
check the 12 volt battery, any major parts store will do this for you! This is a known problem, it will cause a drain on the big battery and cause a MPG average loss. It causes the car to keep trying to charge the 12 volt battery instead of giving you extra electric t0 propel the car. Just my guess, hope this helps.

 

The key symptoms of a failing traction battery (short of multiple warning lights) is large fluctuations in displayed state of charge.
I'm with the others in suspecting a 12V battery failure.

 

Please note that the 12 volt should be checked after the car sits over-night so you can get a good reading/idea of how the battery is holding a charge. Also, the car has to be off or in acc mode when you check it. If not, you will get a false reading...

A reading above 12 is good, above 12.4 is really good. Then, turn on the headlights and see how quickly the voltage drops. A good 12 volt will drop slowly, a bad one will start to drop a tenth at a time every few seconds. Don't let it drop too much, or you won't be able to start the car...

 

Let us know the outcome

 

This myth again !!!!

Let just say that 12V battery is charging so what that can NOT account for 10% MPG loss...

Unless the 12V battery has a cell shorted it would be a load comparable to the two headlights which is a magnitude lower from the load HV battery supplies to MG2 ...

 

It's not a myth if it actually happened to ME in my Gen II. MPG drop, HV not charging properly. 12Volt tested the same way the OP's did. Brought my car to Toyota, and they could NOT find anything wrong. Two weeks later, I performed the 12 Volt test via the maintenance screen and the voltage started to drop as I described above. Dealer changed the battery and confirmed Cell 2 was bad. After the new battery was installed, everything went back to normal... No one can be sure without being there to diagnose it, but it's is quite possible.

 

Let us know what happens...

 

As I said unless a cell (or two) is shorted ... !!! If a cell shorted you will not get even 11.4v more like 10.8

 

Did they perhaps disconnect and reconnect the 12V battery as part of the check, causing things to be reset?

 

When did you say that? I was replying to your quote that the 10% mileage loss is not possible with a 12 Volt Battery... You said it was a myth, and I said, I know it's not a myth, because I lived through it with my '07...

 

just scroll up last paragraph you actually quoted that as well

 

LOL. I thought you meant YOU said it... Whatever... I'm going to wash the 900 love bugs that smashed into my car today...